1. Field of the Invention
The present invention relates to a method of and an apparatus for extruding a billet of a light metal alloy. Specifically, the invention pertains to a method and an apparatus wherein a billet of a light metal alloy can be extruded with a reduced resistance and shaped into a desired configuration of a product under a low extruding force.
2. Description of the Related Art
Heretofore, various methods are known for extruding light metal alloy, such as those disclosed in the following patent documents: U.S. Pat. Nos. 4,550,584, 4,773,251 4,829,802, JP-A-57-7,318, JP-A-4-59,174, JP-A-4-305,311, etc.
Among other things, JP-A-4-59,174 discloses a method wherein light metal alloy is extruded and shaped into a connecting rod. More particularly, a raw material in the form of a billet to be processed, comprising a light metal alloy, is formed into a rod-like body by means of an extrusion die having a die hole which is similar in the outer configuration to a connecting rod, and the so-obtained rod-like body is cut into billets of a predetermined length which are then shaped by a forging die into the connecting rods.
However, there have been such problems with the above-mentioned extrusion method that the raw material billet has an outer diameter which is greater than the maximum configuration width of the die hole of the die and hence an increased cross-sectional area. Due to such problems the extrusion cannot be performed without an increased extrusion pressure to achieve a required load per unit area for the extrusion.